The present invention relates to electric motors and, more particularly, to brushes and brush assemblies.
Electric motors are used in various applications, as well as in a number of work-related areas. One area where small electric motors are utilized is in power tools. A brush is an integral part in transmitting power between a commutator and a power supply.
Various types of mountings which have springs are utilized to exert a force on the brush. The effectiveness of the brush and wear on the brush is decreased when the brush is subjected to arcing. Arcing is inherently present when the brush has a tendency to bounce or move away from the commutator and the brush hits irregularities over rough spots.
Accordingly, it is an object of the present invention to provide the art with a brush and brush assembly which will provide a substantially constant force on the brush. The present invention provides a brush which enables a spring to exert a constant force onto the brush to reduce wear. The brush includes a surface where the resultant spring force applied on the surface, by the assembly spring, is substantially the same throughout the life of the brush. Also, a stop is present on the brush which prohibits undue wear on the brush by prohibiting further travel of the brush towards the commutator. This likewise prevents the shunt wire from engaging the commutator damaging the commutator surface. Further, the stop prohibits the spring from dislodging from the end of the brush.
In accordance with one aspect of the invention, a brush assembly for electric motors comprises a base, the base includes a member for securing the base with a motor spider assembly. A brush housing is associated with the base. The brush housing has first and second open ends. A brush, defining an axis, is movably positioned in the housing between the first and second open ends. The brush extends from one of the open ends of the housing. The brush includes a surface which is at a desired angle with respect to the brush axis. A biasing member exerts a force on the brush. The brush is biased into electrical connection with a commutator. An electrical connector electrically couples with the brush to establish an electrical connection between the commutator and a power supply. Also, the brush includes a recessed portion with the recessed portion including the surface. The brush also includes a stop adjacent to the recessed portion. The housing includes an axial slot in which the stop projects to prohibit further movement of the brush in the housing. The surface is at an angle greater than zero with respect to a plane tangent the brush axis. Preferably, the angle is greater than zero to about ten degrees. The angle is such that the biasing member applies substantially constant force on the brush as the brush wears during use.
In accordance with a second aspect of the invention, a brush for an electric motor comprises a body having a desired configuration adapted for associating with a brush housing. The body defines an axis. A surface is on the body. The surface is on a desired angle with respect to a plane transverse to the axis. Also, the surface is at a terminal end of the body. The angle of the surface is greater than zero. The surface enables a spring force to be exerted on it such that the force is substantially constant as the brush wears. The brush also includes a recessed portion which includes the surface. The brush is a desired cross-sectional configuration and the recessed portion is positioned between a pair of members which extend from sides of the cross-sectional configuration. The angle of the surface is between greater than zero degrees to about ten degrees. A stop is unitarily formed on the brush. The stop is adjacent the recessed portion. The recessed portion extends a desired distance across the brush forming a second recess adjacent the recessed portion. An electrical contact is secured with the brush in the second recess.
In accordance with a third aspect of the invention, a power tool utilizes an electric motor with the above described brush assembly.